Venus Flyby Research Articles

Planetary radio interferometry and Doppler experiment as an operational component of the Jupiter Icy Moons Explorer mission

AbstractWe present an overview of the operations and engineering interface for Planetary Radio Interferometry and Doppler Experiment (PRIDE) radio astronomy observations as a scientific component of the ESA’s Jupiter Icy Moons Explorer (JUICE) mission, as well as other prospective planetary and space science missions. The article discusses advanced scheduling and planning methods that make it possible to create observing schedules for observations of specific spacecraft in concurrence with observations of natural radio sources. In order to put this into practice and find suitable natural background calibrator sources for PRIDE of JUICE mission, we developed planning and scheduling software. The conventional scheduling software for natural celestial radio sources is not set up to include spacecraft as observation targets in the necessary control files. Therefore, difficulties already arise during observation planning. We report on the development of new and the adaptation of existing routines used in astrophysical and geodetic VLBI for satellite scheduling and planning. The analysis of the PRIDE science observations led to improved observational planning, and the mission’s scheduling methodologies were studied using a systems engineering approach. In addition, we highlighted the new procedures, like finding charts for selecting calibrator radio sources over a range of frequency bands and the outcomes of those strategies for science operation planning. A simulation of the flyby of Venus during the cruise phase of the JUICE spacecraft, based on the Tudat software, is also presented, resulting in a promising opportunity to test PRIDE techniques and evaluate the improvements that PRIDE observables can make to natural bodies’ ephemerides. The first $$\hbox {K}_{a}$$ K a -band (32 GHz) observations of the ESA’s BepiColombo by a radio telescope in the VLBI network, which employs a similar radio communications system as JUICE, were also demonstrated as a test case. The primary objective of these activities is to serve as a practice run for the upcoming operational PRIDE JUICE operations. We showcase the capabilities of the planning and scheduling software for other space missions.

Closed magnetic topology in the Venusian magnetotail and ion escape at Venus

Venus, lacking an intrinsic global dipole magnetic field, serves as a textbook example of an induced magnetosphere, formed by interplanetary magnetic fields (IMF) enveloping the planet. Yet, various aspects of its magnetospheric dynamics and planetary ion outflows are complex and not well understood. Here we analyze plasma and magnetic field data acquired during the fourth Venus flyby of the Parker Solar Probe (PSP) mission and show evidence for closed topology in the nightside and downstream portion of the Venus magnetosphere (i.e., the magnetotail). The formation of the closed topology involves magnetic reconnection—a process rarely observed at non-magnetized planets. In addition, our study provides an evidence linking the cold Venusian ion flow in the magnetotail directly to magnetic connectivity to the ionosphere, akin to observations at Mars. These findings not only help the understanding of the complex ion flow patterns at Venus but also suggest that magnetic topology is one piece of key information for resolving ion escape mechanisms and thus the atmospheric evolution across various planetary environments and exoplanets.

BepiColombo observations of cold oxygen and carbon ions in the flank of the induced magnetosphere of Venus

On 10 August 2021, the Mercury-bound BepiColombo spacecraft performed its second fly-by of Venus and provided a short-lived observation of its induced magnetosphere. Here we report results recorded by the Mass Spectrum Analyzer on board Mio, which reveal the presence of cold O+ and C+ with an average total flux of ~4 ± 1 × 104 cm−2 s−1 at a distance of about six planetary radii in a region that has never been explored before. The ratio of escaping C+ to O+ is at most 0.31 ± 0.2, implying that, in addition to atomic O+ ions, CO group ions or water group ions may be a source of the observed O+. Simultaneous magnetometer observations suggest that these planetary ions were in the magnetosheath flank in the vicinity of the magnetic pileup boundary downstream. These results have important implications regarding the evolution of Venus’s atmosphere and, in particular, the evolution of water on the surface of the planet.

Electron moments derived from the Mercury Electron Analyzer during the cruise phase of BepiColombo

Aims. We derive electron density and temperature from observations obtained by the Mercury Electron Analyzer on board Mio during the cruise phase of BepiColombo while the spacecraft is in a stacked configuration. Methods. In order to remove the secondary electron emission contribution, we first fit the core electron population of the solar wind with a Maxwellian distribution. We then subtract the resulting distribution from the complete electron spectrum, and suppress the residual count rates observed at low energies. Hence, our corrected count rates consist of the sum of the fitted Maxwellian core electron population with a contribution at higher energies. We finally estimate the electron density and temperature from the corrected count rates using a classical integration method. We illustrate the results of our derivation for two case studies, including the second Venus flyby of BepiColombo when the Solar Orbiter spacecraft was located nearby, and for a statistical study using observations obtained to date for distances to the Sun ranging from 0.3 to 0.9 AU. Results. When compared either to measurements of Solar Orbiter or to measurements obtained by HELIOS and Parker Solar Probe, our method leads to a good estimation of the electron density and temperature. Hence, despite the strong limitations arising from the stacked configuration of BepiColombo during its cruise phase, we illustrate how we can retrieve reasonable estimates for the electron density and temperature for timescales from days down to several seconds.

The second Venus flyby of BepiColombo mission reveals stable atmosphere over decades

Studies of the Venusian mesosphere provide important information about the current state of the entire Venusian atmosphere. This includes information about the dense cloud structure, its vertical thermal profile, temperature fields, and the resulting dynamical and meteorological processes that contribute to a deeper understanding of the climatologically different evolutionary paths of Earth and Venus. However, the last measurements were acquired in 1983 during Venera-15 mission. In this paper, results of mid-infrared spectral measurements of the Venusian atmosphere are presented. Here we show Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) measurements of the Venusian atmosphere during the second flyby of BepiColombo mission on its way to Mercury. Our Venus measurements provide reliable retrievals of mesospheric temperature profiles and cloud parameters between 60 and 75 km altitude, although MERTIS was only designed to operate in Mercury environment. Our results are in good agreement with the Venera-15 mission findings. This indicates the stability of the Venusian atmosphere on time scales of decades.

A WISPR of the Venus Surface: Analysis of the Venus Nightside Thermal Emission at Optical Wavelengths

Parker Solar Probe (PSP) conducted several flybys of Venus while using Venus’ gravity for orbital adjustments to enable its daring passes of the Sun. During these flybys, PSP turned to image the nightside of Venus using the Wide-field Imager for Solar PRobe (WISPR) optical telescopes, which unexpectedly observed Venus’ surface through its thick and cloudy atmosphere in a theorized, but until-then unobserved near-visible spectral window below 0.8 μm. We use observations taken during PSP’s fourth Venus gravity assist flyby to examine the origin of the Venus nightside flux and confirm the presence of this new atmospheric window through which to observe the surface geology of Venus. The WISPR images are well explained by emission from the hot Venus surface escaping through a new atmospheric window in the optical with an overlying emission component from the atmosphere at the limb that is consistent with O2 nightglow. The surface thermal emission correlates strongly with surface elevation (via temperature) and emission angle. Tessera and plains units have distinct WISPR brightness values. Controlling for elevation, Ovda Regio tessera is brighter than Thetis Regio; likewise, the volcanic plains of Sogolon Planitia are brighter than the surrounding regional plains units. WISPR brightness at 0.8 μm is predicted to be positively correlated to FeO content in minerals; thus, the brighter units may have a different starting composition, be less weathered, or have larger particle sizes.

Flying Parker Solar Probe to touch the Sun

For the first time in history, Parker Solar Probe touched the Sun in April 2021 when it entered the Sun's corona—humanity's first mission ever that reached the Sun—for a scientific in-situ study to unlock the mystery of our star. To reach the Sun is extremely difficult because, unlike any other space exploration destination, the Sun is the solar system's central body, around which Earth and other planets revolve. Earth orbits the Sun at a velocity of about 30 km/s, so for a spacecraft to reach the Sun from Earth the spacecraft must cancel out its velocity in the Earth orbit so it can fall to the Sun. That requires an excessively large energy higher than that required to reach any destination in the solar system, which is beyond the capability of current rockets. This paper describes how Parker Solar Probe is delivered to the Sun through a unique V7GA trajectory that enables it to attain the excessive energy through planetary gravity assists of Venus, flying by Venus seven times to ultimately come within 9.86 solar radii (RS) of the Sun. An emphasis is on in-flight trajectory control of the probe through the intricate V7GA trajectory in actual operation in an unprecedented space environment around the Sun, where unpredictable orbit perturbations plus their ripple effects on the consecutive seven Venus flybys could easily drive the flight trajectory out of control. A novel systematic 2-level control method is developed and has been applied to solve the complicated trajectory control problem in flight operation, using in-flight trajectory re-optimization to select the targets of Venus flybys as trajectory control points and then using trajectory correction maneuvers to target a Venus flyby at the control point. This method enables effective and efficient control of the intricate V7GA trajectory and has resulted in significantly better than pre-launch anticipated flight performance, saving tremendous ΔV. Four years from launch, Parker Solar Probe has completed 5 of the 7 Venus gravity-assist flybys and 12 of the 24 planned solar encounters, passing by the Sun at 13 RS in its orbit. Flight results and performance of the completed flight to date are also described.

Analysis of prospective flight schemes to Venus accompanied by an asteroid flyby

This paper deals with the problem of constructing a flight scheme to Venus, in which a spacecraft flying to the planet after a gravity assist maneuver and transition to a resonant orbit in order to re-encounter with Venus, makes a passage of a minor celestial body. The 117 candidate asteroids from the NASA JPL catalogue, whose diameter exceeds 1 km, were selected. The flight trajectories which meet the criteria of impulse-free both flyby Venus and asteroid, and the subsequent landing on the surface of Venus were found within the interval of launch dates from 2029 to 2050. The trajectory of the spacecraft flight from the Earth to Venus including flyby of Venus and asteroids with a subsequent landing on the surface of Venus was analyzed.

Solar Orbiter Data‐Model Comparison in Venus' Induced Magnetotail

AbstractWe investigate the structure of the Venusian magnetotail utilizing magnetic field and electron density measurements that cover a wide range of distances from the planet, from the first two Solar Orbiter Venus flybys. We examine the magnetic field components along the spacecraft trajectory up to 80 Venus radii down the tail. Even though the magnetic field behavior differs considerably between the two cases, we see extended electron density enhancements covering distances greater than ∼20 RV in both flybys. We compare the magnetic field measurements with a global hybrid model of the induced magnetosphere and magnetotail of Venus, to examine to what degree the observations can be understood with the simulation. The model upstream conditions are stationary and the solution encloses a large volume of 83 RV × 60 RV × 60 RV in which we look for spatial magnetic field and plasma variations. We rotate the simulation solution to describe different stationary upstream IMF clock angle cases with a 10° step and find the clock angle for which the agreement between observations and model is maximized along Solar Orbiter's trajectory in 1‐min steps. We find that in both flybys there is better agreement with the observations when we rotate the model for some intervals, while there are parts that cannot be well reproduced by the model irrespective of how we vary the IMF clock angle, suggesting the presence of non‐stationary features in the Venus‐solar wind interaction not accounted for in the hybrid model.

BepiColombo mission confirms stagnation region of Venus and reveals its large extent

The second Venus flyby of the BepiColombo mission offer a unique opportunity to make a complete tour of one of the few gas-dynamics dominated interaction regions between the supersonic solar wind and a Solar System object. The spacecraft pass through the full Venusian magnetosheath following the plasma streamlines, and cross the subsolar stagnation region during very stable solar wind conditions as observed upstream by the neighboring Solar Orbiter mission. These rare multipoint synergistic observations and stable conditions experimentally confirm what was previously predicted for the barely-explored stagnation region close to solar minimum. Here, we show that this region has a large extend, up to an altitude of 1900 km, and the estimated low energy transfer near the subsolar point confirm that the atmosphere of Venus, despite being non-magnetized and less conductive due to lower ultraviolet flux at solar minimum, is capable of withstanding the solar wind under low dynamic pressure.

Reflectivity of Venus’s Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns.

LatHyS global hybrid simulation of the BepiColombo second Venus flyby

Plasma and magnetic field observations by BepiColombo during its 2nd Venus flyby in August 10, 2021 have been examined and compared with the newly developed global hybrid simulation LatHyS for the Venusian environment. The LatHyS-Venus simulation was first validated by a comparison with Venus Express observations obtained during average solar wind conditions, before it was applied to the BepiColombo flyby using as inputs solar wind parameters measured upstream of Venus by Solar Orbiter. The simulation confirms that BepiColombo passed through the stagnation region of Venus, which supports the results obtained by data analysis. In addition, we have sampled the plasma parameters along the BepiColombo trajectory and constructed the energy spectrum for two species, i.e., protons of both solar wind and planetary origins, and planetary oxygen ions, and discussed the possible effects due to the limited field of views of the plasma instruments onboard BepiColombo. The most intense observational features are properly captured in the LatHyS-Venus simulation, which show that the model is a powerful tool for interpreting and understanding in-situ data obtained from the instruments with a limited field of views. The estimated ion escape for protons and oxygen ions at Venus during the BepiColombo flyby is of the order of ∼ 10 24 ions/s, which is the same order of magnitude compared to the estimation from Venus Express observations at the solar minimum. 1) We have developed the global hybrid simulation for the Venusian environment. 2) Observations by BepiColombo during its 2nd Venus flyby in August 10, 2021 have been examined. 3) The possible effects due to the limited field of views of the plasma instruments onboard BepiColombo have been discussed by sampling plasmas in the simulation domain.

Concept for 2033 Crewed Mars Orbital Mission with Venus Flyby

The 2033 Mars launch period provides a unique opportunity for a round-trip mission with a total flight time of only 1.6 years. A concept is presented to perform a crewed Mars orbital mission in 2033 that would minimize development and mission risk by using conventional hypergolic in-space propulsion stages with a common design. The Mars mission vehicle would include a Mars transit habitat, an Orion spacecraft, and chemical propulsion stages. It would be launched by a combination of Space Launch System and commercial rockets to be aggregated in high Earth orbit or at the Lunar Gateway. The crew would launch to the mission vehicle in Orion as the final element in the assembly. After transit to Mars, the crew would spend about 30 days in a high Mars orbit and then return to Earth via a Venus flyby and gravity assist. A sunshade would be deployed for thermal control of the mission vehicle inside 1 astronomical unit. The crew would return directly to Earth in the Orion crew module, with the transit habitat being expended. The 2033 mission would not be a “one-off” but could be a pathfinder for crew transport for landing missions to follow, perhaps starting as early as 2037.

B-plane and Picard–Chebyshev integration method: Surfing complex orbital perturbations in interplanetary multi-flyby trajectories

Orbital resonances have been exploited in different contexts, with the latest interplanetary application being the ESA/NASA mission Solar Orbiter, which uses repeated flybys of Venus to change the ecliptic inclination with low fuel consumption. The b-plane formalism is a useful framework to represent close approaches at the boundaries of the sphere of influence of the flyby planet. In the presented work, this representation is exploited to prune the design of perturbed resonant interplanetary trajectories in a reverse cascade, replacing the patched conics approximation with a continuity link between flybys and interplanetary legs. The design strategy splits the flyby time and state variables in a two-layer optimization problem. Its core numerically integrates the perturbed orbital motion with the Picard–Chebyshev integration method. The analytical pruning provided by the b-plane formalism is also used as starting guess to ensure the fast convergence of both the numerical integration and the trajectory design algorithm. The proposed semi-analytical strategy allows to take advantage of complex gravitational perturbing effects optimizing artificial maneuvers in a computationally efficient way. The method is applied to the design of a Solar Orbiter-like quasi-ballistic first resonant phase with Venus.

Parker Solar Probe Imaging of the Night Side of Venus.

We present images of Venus from the Wide‐Field Imager for Parker Solar Probe (WISPR) telescope on board the Parker Solar Probe (PSP) spacecraft, obtained during PSP's third and fourth flybys of Venus on 2020 July 11 and 2021 February 20, respectively. Thermal emission from the surface is observed on the night side, representing the shortest wavelength observations of this emission ever, the first detection of the Venusian surface by an optical telescope observing below 0.8 μm. Consistent with previous observations at 1 μm, the cooler highland areas are fainter than the surrounding lowlands. The irradiances measured by WISPR are consistent with model predictions assuming a surface temperature of T = 735 K. In addition to the thermal emission, the WISPR images also show bright nightglow emission at the limb, and we compare the WISPR intensities with previous spectroscopic measurements of the molecular oxygen nightglow lines from Venus Express.

A Revised Understanding of the Structure of the Venusian Magnetotail From a High‐Altitude Intercept With a Tail Ray by Parker Solar Probe

AbstractOne of the major discoveries of NASA's 1979–1991 Pioneer Venus Orbiter is that the nightside ionosphere becomes filamentary at high altitude, forming comet‐like tail rays. Pioneer Venus Orbiter could not establish how much farther into the wake of Venus tail rays extend, nor understand how they form. Here we present plasma and fields data from the fourth flyby of Venus by NASA's Parker Solar Probe consistent with an intercept with an ionospheric tail ray. The observations unambiguously demonstrate that Venusian Ionotail Rays can extend to at least 7,800 km in altitude. Using the new Parker observations we are able to identify a tail ray encounter within the Venus Express dataset. We thus present a unified picture of the structure of the magnetotail of Venus based on combined Venus Express, Pioneer Venus Orbiter, and Parker observations, and recent hybrid modeling.

First-year ion-acoustic wave observations in the solar wind by the RPW/TDS instrument on board Solar Orbiter

Context.Electric field measurements of the Time Domain Sampler (TDS) receiver, part of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter, often exhibit very intense broadband wave emissions at frequencies below 20 kHz in the spacecraft frame. During the first year of the mission, the RPW/TDS instrument was operating from the first perihelion in mid-June 2020 and through the first flyby of Venus in late December 2020.Aims.In this paper, we present a year-long study of electrostatic fluctuations observed in the solar wind at an interval of heliocentric distances from 0.5 to 1 AU. The RPW/TDS observations provide a nearly continuous data set for a statistical study of intense waves below the local plasma frequency.Methods.The on-board and continuously collected and processed properties of waveform snapshots allow for the mapping plasma waves at frequencies between 200 Hz and 20 kHz. We used the triggered waveform snapshots and a Doppler-shifted solution of the dispersion relation for wave mode identification in order to carry out a detailed spectral and polarization analysis.Results.Electrostatic ion-acoustic waves are the most common wave emissions observed between the local electron and proton plasma frequency by the TDS receiver during the first year of the mission. The occurrence rate of ion-acoustic waves peaks around perihelion at distances of 0.5 AU and decreases with increasing distances, with only a few waves detected per day at 0.9 AU. Waves are more likely to be observed when the local proton moments and magnetic field are highly variable. A more detailed analysis of more than 10 000 triggered waveform snapshots shows the mean wave frequency at about 3 kHz and wave amplitude about 2.5 mV m−1. The wave amplitude varies asR−1.38with the heliocentric distance. The relative phase distribution between two components of the E-field projected in theY − ZSpacecraft Reference Frame (SRF) plane shows a mostly linear wave polarization. Electric field fluctuations are closely aligned with the directions of the ambient field lines. Only a small number (3%) of ion-acoustic waves are observed at larger magnetic discontinuities.

Energetic ions in the Venusian system: Insights from the first Solar Orbiter flyby

The Solar Orbiter flyby of Venus on 27 December 2020 allowed for an opportunity to measure the suprathermal to energetic ions in the Venusian system over a large range of radial distances to better understand the acceleration processes within the system and provide a characterization of galactic cosmic rays near the planet. Bursty suprathermal ion enhancements (up to ∼10 keV) were observed as far as ∼50RVdowntail. These enhancements are likely related to a combination of acceleration mechanisms in regions of strong turbulence, current sheet crossings, and boundary layer crossings, with a possible instance of ion heating due to ion cyclotron waves within the Venusian tail. Upstream of the planet, suprathermal ions are observed that might be related to pick-up acceleration of photoionized exospheric populations as far as 5RVupstream in the solar wind as has been observed before by missions such as Pioneer Venus Orbiter and Venus Express. Near the closest approach of Solar Orbiter, the Galactic cosmic ray (GCR) count rate was observed to decrease by approximately 5 percent, which is consistent with the amount of sky obscured by the planet, suggesting a negligible abundance of GCR albedo particles at over 2RV. Along with modulation of the GCR population very close to Venus, the Solar Orbiter observations show that the Venusian system, even far from the planet, can be an effective accelerator of ions up to ∼30 keV. This paper is part of a series of the first papers from the Solar Orbiter Venus flyby.

Future Venus missions and flybys: A collection of possible measurements with mass spectrometers and plasma instruments

This study contains predictions for mass spectrometry and plasma instrument measurements during upcoming Venus flybys of BepiColombo and Solar Orbiter and discusses the possibility of a phosphine detection with mass spectrometry in Venus’ upper atmosphere. The results extend the ones published previously in Gruchola et al. (2019) , where predictions for the proposed ESA mission EnVision and the Venus flyby of JUICE were included. Both the Venus flyby of BepiColombo and the one of Solar Orbiter will take place in August 2021, only 1 day apart. BepiColombo, carrying the neutral mass gas spectrometer STROFIO, could probe the atmosphere around closest approach and obtain data on the thermal and hot neutral particle populations in the upper atmosphere. According to this study, the thermal hydrogen population as well as the hot species H, C, N and O, including isotopes, should be visible to STROFIO. Especially data on the abundance of the hot species would yield important insight into the planetary escape processes. The Solar Orbiter on the other hand carries the plasma instrument SWA-HIS, designed to measure the energetic solar wind ions. During its second Venus gravity assist it will traverse the magnetosheath, the region between bow shock and ion composition boundary, where in addition to the solar wind ions energetic planetary ions are present. The planetary pickup ions can be measured by SWA-HIS, providing important information on the outflow of planetary ions and the ionization processes in the upper atmosphere itself. The recent reports of phosphine in Venus’ cloud decks with an abundance of 20 ppb at 80 km probably overestimate the actual PH 3 abundance, as the data are currently being reanalyzed (Greaves et al., 2021). However, even with this upper limit of 20 ppb a phosphine detection with a mass spectrometer e.g. on-board ESA’s proposed EnVision mission, seems unlikely. To resolve the PH 3 peak and the 16 O 18 O peak a mass resolution of almost 10’000 is required, and the PH 2 D peak is masked by the Cl fragment peak of HCl. Furthermore, NGMS on-board Pioneer Venus with a mass resolution of around 440 did most likely not detect phosphine, as it scanned only a few masses in the mass range of interest where more abundant species than phosphine are present.

Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby

Abstract. Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (SERENA-PICAM) of the SERENA suite, the Mercury Electron Analyser (MEA), and the BepiColombo Radiation Monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with e.g. strong flapping motions at a period of ∼7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.